Magnetically heated susceptor

ABSTRACT

A method and apparatus are provided for heating a solid material and dispensing the material as a liquid. A central housing has an inlet, a dispensing orifice and a flow passage extending through the central housing for passing the material from the inlet to the dispensing orifice. A susceptor and induction coil are disposed within the flow passage for immersion within the material after it is liquified. The susceptor includes a conically shaped flow section which extends across the flow passage, and a plurality of flow ports for passing the material. The susceptor further includes a cylindrical section which extends downstream from the flow section for receiving the material from the flow section and passing material to the dispensing orifice. The induction coil is aligned with and spaced downstream from the flow section of the susceptor, surrounding part of the susceptor for electromagnetically inducing electric currents to flow within the flow section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to heating and dispensing materials,and in particular to devices for electromagnetically heating anddispensing materials.

2. Description of the Prior Art

Prior art devices have been utilized for heating and dispensingmaterials, such as for heating a solid material until it melts and thendispensing the material as a liquid. For example, hot glue guns are usedfor heating an end of a solid glue stick to a transition temperature atwhich the glue is liquefied and then dispensing the melted glue througha dispensing orifice. Typically, a housing is provided having aninterior flow path through which the material is pushed as it is heated.Resistance heating elements are commonly used. The resistance heatingelements have been mounted to the housing outside of the flow path, andoften outside of the housing.

Other devices have utilized induction heating to heat materials fordispensing. A housing is usually provided having an interior flow paththrough which the material is pushed as it is heated. Anelectromagnetically heated susceptor is located either directly in orimmediately adjacent to the material flow path. Induction coils havebeen mounted outside of the housings for inducing eddy currents to flowwithin the susceptors to generate heat for transferring to thematerials. Often an external shroud is provided around the inductioncoil to protect an operator. Heat from passing current through theinduction coil usually has to be removed to prevent overheating of thecoil. Forced cooling is often used, resulting in wasted energy. Externalshrouds and cooling devices for induction coils also add additionalweight and size to such prior art devices.

Inductive heating devices having large material flow capacities requirethat a large surface of the material be heated at one time. For meltingmaterials, this results in susceptors having large heat transfer surfaceareas for contacting materials at melt faces for the materials. In orderto prevent cold spots over the large heat transfer surface areas of suchsusceptors, the susceptors are made to have high heat capacities andhigh thermal conductivities. Although susceptors having high heatcapacities in combination with high thermal conductivities addadditional weight to prior art devices, they provide substantiallyuniform temperatures across the heat transfer surface areas, even thoseportions of the surface areas which are more remote from induction coilsthan others. However, when inductive heating of the susceptor isstopped, the large heat capacity of such susceptors will result incontinued heat transfer to the material, often to a significant depthwithin the material beyond the melt face. This not only wastes energy,but may also result in waste of the material being heated.

SUMMARY OF THE INVENTION

A method and apparatus are provided for heating and dispensing amaterial. A central housing has an inlet, a dispensing orifice and aflow passage extending through the central housing for passing thematerial from the inlet to the dispensing orifice. A susceptor andinduction coil are disposed within the flow passage for immersing withinthe material. The susceptor includes a conically shaped flow sectionwhich extends across the flow passage, and a plurality of flow ports forpassing the material. The susceptor further includes a cylindricalsection which extends downstream from the flow section for receiving thematerial from the flow section and passing material to the dispensingorifice. The induction coil is aligned with and spaced downstream fromthe flow section of the susceptor, surrounding part of the susceptor forelectromagnetically inducing electric currents to flow within the flowsection. The induced electric currents are substantially uniform acrossthe flow section to provide a substantially uniform thermal transferfrom the flow section to a melt face for the material. The flow sectionhas a limited heat capacity such that the flow section will not containan amount of heat sufficient to significantly raise the temperature ofthe material adjacent to the flow section when the electric currents arestopped, preventing thermal transfer from the susceptor to a significantportion of the material beyond the melt face.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself however, as well as apreferred mode of use, further objects and advantages thereof, will bestbe understood by reference to the following detailed description of anillustrative embodiment when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a side elevational and partial section view of a hot glue gunhaving an electromagnetically heated susceptor made according to thepresent invention;

FIG. 2 is a partial longitudinal section view depicting the nozzle tipof the hot glue gun of FIG. 1 in more detail;

FIG. 3 is sectional view taken along section line 3--3 of FIG. 2, anddepicts the rearward facing end of the susceptor; and

FIG. 4 is a schematic diagram illustrating an electromagnetic circuitfor a power supply, an induction coil and a susceptor for the hot gluegun of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a side elevational view of hot glue gun 11 of the presentinvention. Gun 11 is used for heating, liquefying and dispensing solidsticks of glue which nominally measure two (2) inches in diameter andeight (8) inches in length. Gun 11 has a body 13 and a nozzle tip 15.Grip handle 17 is provided for holding gun 11, and includes a triggertype of button 19 for controlling heating and dispensing of the hotglue. Power cord 21 extends from handle 17 and connects to power supply23, which preferably is a 110 volt AC source.

Feed assembly 25 provides a means for pushing a glue stick into nozzletip 15. Feed assembly 25 includes a stepper motor 27 which is connectedby means of gear 29 to rack 31. Stepper motor 27 and gear 29 are mountedto driven member 33, which is moved in direction 34 within cavity 35. Anintermediate position for driven member 33, stepper motor 27 and gear 29is depicted in FIG. 1. A rearward position 36 is depicted in phantom fordriven member 33, stepper motor 27 and gear 29. Glue stick 37 is placedin cavity 35, forward of driven member 33. Glue stick 37 has a forwardend 39 for pressing into nozzle tip 15. Stepper motor 27 is actuated tomove driven member 33 forward in direction 34, from position 36 to theintermediate position depicted in FIG. 1. This presses the forward face39 of glue stick 37 into the rearward end of susceptor 53.

FIG. 2 is a sectional view depicting nozzle tip 15 in more detail.Nozzle 41 is formed from aluminum and has a dispensing orifice 43. Ahousing 45 of a plastic material, such as teflon, extends rearward ofnozzle 41, and has a conical shape. A cylindrical member 47 extendsrearward of housing 45. Nozzle 41, housing 45, and cylindrical member 47together define a central housing 49 having interior bore 51. Bore 51provides a flow passage for passing glue through housing 49.

Susceptor 53 extends within housing 49, across a rearward section ofbore 51. Susceptor 53 includes a conical flow section 55, having a thincross section with a heat capacity which is not substantially greaterthan a thin section of the material extending across the melt face atforward end 39 of glue stick 37. Conical flow section 55 has an outerdiameter of two (2) inches. Holes 57 extend through the rearward portionof susceptor 53 to provide flow ports through flow section 55. Holes 57are parallel to central longitudinal axis 58.

FIG. 3 is a sectional view taken along section line 3--3 of FIG. 2, anddepicts holes 57 extending through the conically shaped, rearward facingend of susceptor 53. In this embodiment of the present invention,approximately 51% of the rearward facing surface end of susceptor 53 isholes, providing a reduced heat capacity for susceptor 53. The solidportion 60 of the conically shaped, rearward facing end of susceptor 53contacts forward face 39 of material 37 to define a melt face. The meltface also extends within holes 57 when solid material is pushed intoholes 57. Thus the effective heat transfer surface area for susceptor 53at the melt face includes both solid portion 60 of the rearward facingend of susceptor 53 and at least a portion of the periphery of holes 57.

Referring to FIG. 2, susceptor 53 further includes cylindrical section59 and thermal transfer member 61. In the preferred embodiment, flowsection 55 and cylindrical section 59 are formed from various materialswithin which an electric current can be electromagnetically induced toflow. Thermal transfer member 61 is formed from a non-ferrous material,and provides a means for transmitting electromagnetically induced heatforward from the rearward portion of flow section 55 so that restartingof glue flow from gun 11 can be more quickly accomplished than if member61 were not included. The components of susceptor 53 may be formed ofother materials, so long as flow section 55 is formed from materialswithin which may be electromagnetically heated by inducing eddy currentsto flow therein.

The exterior of cylindrical section 59 is threaded. The rearward end ofnozzle 41 is threaded and secures to cylindrical section 59, and theforward end of housing 45 is also threaded for coupling to cylindricalsection 59. Cylindrical section 59 will conduct high frequency electriccurrent from flow section 55 to nozzle 41, which is also conductive.

Annular space 63 extends between cylindrical section 59 and thermaltransfer member 61 of susceptor 53. Four flow ports 65 and four flowports 67 extend through cylindrical section 59 to connect annular space63 to annular space 69, which extends between housing 45 and flowsection 55. Flow ports 65, 67 are offset both angularly andlongitudinally along a central axis for central housing 49. Annularspace 69 has a conical shape, which extends with a narrower width atoutermost portion 71 than at inner portion 73. Inner portion 73 is widerto provide a constant cross sectional flow area per unit amount of glueflowing through annular space 69. Annular space 69 is formed betweenhousing 45 and flow section 55 of susceptor 53. The forward face of flowsection 55 is at a 45 degree angle to central longitudinal axis 58 forflow passage 51 in central housing 49. The interior, conically shapedsurface of housing 45 is at a 30 degree angle to longitudinal axis 58for flow passage 51 and central housing 49.

Induction coil 75 is conically shaped and located within conicallyshaped annular space 69. Forward end 77 of coil 75 is welded to theforward end for flow section 55 of susceptor 53. Wire 79 extends fromthe rearward end of coil 75 to electrically connect coil 75 to powersupply 23 (shown in FIG. 1). Wire 81 extends through housing 45 toground screw 83 and nozzle 41. This provides an electrical connectionfor connecting power supply 23 to the forward end 77 of coil 75, whichis welded to susceptor 53. Susceptor 53 will conduct the high frequencycurrent to nozzle 41 and ground screw 83.

FIG. 4 is a schematic diagram depicting an electromagnetic circuit whichincludes power supply 23, susceptor 53 and induction coil 75. Powersupply 23 includes high frequency power supply 85 which is connected bymeans of power cord 21 to an external power source. Power supply 23nominally operates at frequencies of 50 kHz, with the frequencytypically being lowered for susceptors of larger dimension, and can bepowered from a 20 amp 110 volt a.c. outlet. Transformer 87 iselectrically connected between high frequency power supply 85 andinduction coil 75 by means of wires 79, 81. Thermocouple 89 is providedfor controlling the temperature of susceptor 53. Power supply 23 has avariable temperature set point for accommodating glues of differentmelting temperatures.

Referring to FIG. 2, in operation, high frequency electrical currentflowing through induction coil 75 causes an electromagnetic field,depicted as the lines of electromagnetic flux 91 passing throughsusceptor 53. Electromagnetic flux 91 causes eddy currents to flowwithin susceptor 53, which generate heat. The forward end 39 of gluestick 37 is pressed inward to susceptor 53 by feed assembly 25 (shown inFIG. 1). This causes the end face 39 of glue stick 37 to melt and flowthrough ports 57 into conically shaped annular space 69. The melted gluethen flows from annular space 69 through flow ports 65, 67, intocylindrically shaped annular space 63, and through dispensing orifice 43of nozzle 41. Melted glue flowing past induction coil 75 removes heatfrom coil 75, cooling coil 75. It should be noted that thecross-sectional flow area for the total combined flow ports 57 insusceptor 53 is equal to the effective cross-sectional flow area ofannular space 69, flow port 65, 67, and annular space 63 after coil 75and susceptor 53 are installed within central housing 49. This preventsflow restrictions from occurring as the melted glue passes through flowpassage 51.

It should be noted that after holes 57 are formed into flow section 55,the heat capacity for flow section 55 is limited such that it is capableof only containing enough heat for melting only a very fine, thin layerof the face 39 of glue stick 37. The low heat capacity for flow section55 will not contain an amount of heat sufficient to raise thetemperature of a significant portion of the glue material adjacent tothe flow section beyond the melt-phase transition temperature, that isbeyond the temperature at which the glue melts. This provides for a veryfinely controlled, thin melt face for glue stick 37. Thus, once the highfrequency electric current is turned off from flowing within inductioncoil 75, the glue at melt face 39 almost immediately stops melting.

Cylindrical section 59 is formed from a ferrous material and receivessome of the electromagnetic field flux 91 from induction coil 75. Thiscauses eddy currents to flow in cylindrical section 59, generating heatfor transferring to the material adjacent to section 59 in annular space63. Additionally, thermal transfer member 61 transfers heat to the gluewithin annular space 63 to help liquefy the material to initiate flow asglue gun 11 is cycled back on to dispense more glue through orifice 43.Heat from coil 75 and heat induced within flow section 55 will quicklyliquefy any glue that solidifies within annular space 69 when gun 11 iscycled off.

Other embodiments of the present invention may be made for heating anddispensing materials. It should be noted that in other embodiments ofthe present invention, susceptors may be made from materials other thanferrous materials, such as ceramic and carbon materials capable ofhaving electric currents induced to flow therein. One such example is asusceptor having a carbon core which is coated with silicon carbide.Such materials will allow use of the present invention at temperatureswhich are much higher than those for melting glue.

The present invention provides several advantages over prior art devicesfor heating and dispensing materials, such as glue. The presentinvention provides a very finely controlled, thin melt face transitionby providing a susceptor having a low heat capacity so that any thermaltransfer from the susceptor to the melt face will be quickly absorbed bythe adjacent material at the melt face. Also, the induction coilaccording to the present invention surrounds and extends along a portionof the susceptor so that uniform currents can be generated acrossdifferent sections of the susceptor. The induction coil is within a flowpassage and immersed within the material to both cool the induction coiland use heat which is normally lost by exteriorly mounted inductioncoils. Additionally, a thermal transfer member extends forward of theflow section of the susceptor for transferring induced heat forward toimprove recovery times when material flow is cycled back on.

Although the invention has been described with reference to a specificembodiment, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiment as well asalternative embodiments of the invention will become apparent to personsskilled in the art upon reference to the description of the invention.It is therefore contemplated that the appended claims will cover anysuch modifications or embodiments that fall within the true scope of theinvention.

I claim:
 1. An apparatus for heating and dispensing a material, theapparatus comprising in combination:a central housing having an inlet, adispensing orifice, and a flow passage extending through the centralhousing for passing the material from the inlet to the dispensingorifice; a susceptor disposed within the flow passage and in thematerial; and an induction coil disposed within flow passage forimmersion in the material, and disposed proximate to the susceptor forelectromagnetically inducing the susceptor to heat the material.
 2. Theapparatus according to claim 1, wherein the susceptor comprises:a flowsection which extends across the flow path having a plurality of flowports for passing the material therethrough; and wherein the inductioncoil electromagnetically induces electric currents to flow within theflow section, which generates and transfers heat to the material passingthrough the flow ports.
 3. The apparatus according to claim 1, whereinthe susceptor comprises:a flow section having a conical shape whichextends across the flow path and which converges toward the dispensingorifice, and the flow section further having a plurality of flow portsfor passing the material therethrough; a cylindrical section whichextends downstream of the flow section for receiving the material fromthe flow section and passing the material to the dispensing orifice; andwherein the induction coil electromagnetically induces electric currentsto flow within both the flow section and the cylindrical section, whichgenerates and transfers heat to the material passing through the flowsection and the cylindrical section.
 4. The apparatus according to claim1, wherein:the susceptor includes a flow section which extends acrossthe flow path and has a plurality of flow ports for passing the materialtherethrough; and the induction coil is aligned with and spaceddownstream from the flow section of the susceptor forelectromagnetically inducing electric currents to flow within the flowsection which provide substantially uniform thermal transfer across theflow section to the material passing through the flow ports.
 5. Theapparatus according to claim 1, wherein:the susceptor has an axis andincludes a flow section which extends across the flow path, and the flowsection has a plurality of flow ports for passing the materialtherethrough; and the induction coil has an axis that is coaxial withthe axis of the susceptor and the induction coil surrounds at least aportion of the susceptor for electromagnetically inducing substantiallyuniform electric currents to flow across the flow section.
 6. Theapparatus according to claim 1, wherein:the susceptor includes a flowsection which extends across the flow path and has a plurality of flowports for passing the material therethrough; and the flow section has aheat capacity such that the flow section will not contain an amount ofheat sufficient to raise the temperature of a significant portion of thematerial adjacent to the flow section beyond a transition temperature.7. The apparatus according to claim 1, further comprising:a thermaltransfer member formed from a non-ferrous material and extending withinthe flow passage, downstream of the susceptor, for transferring heatfrom the susceptor to a portion of the material after is passes throughthe susceptor.
 8. The apparatus according to claim 1, wherein thesusceptor comprises:a thin conical section which extends across the flowpath and has a plurality of flow ports for passing the materialtherethrough, with the thin conical section converging toward thedispensing orifice; a cylindrical section which extends downstream ofthe thin conical section for receiving the material from the thinconical section and passing the material to the dispensing orifice;wherein the induction coil electromagnetically induces electric currentsto flow within both the thin section and the cylindrical section, whichgenerates and transfers heat to the material passing through the flowports of the thin conical section and the cylindrical section; andwherein the apparatus further comprises a thermal transfer member formedfrom a non-ferrous material and extending within the flow passage,downstream of the susceptor, for transferring heat from the susceptor toa portion of the material after is passes through the susceptor.
 9. Theapparatus according to claim 1, wherein:the susceptor has a flow sectionwhich extends across the flow path and has a plurality of flow ports forpassing the material therethrough; wherein the flow section has a heatcapacity such that the flow section will not contain an amount of heatsufficient to raise the temperature of a significant portion of thematerial adjacent to the flow section beyond a transition temperature;the induction coil is disposed within the flow passage downstream from,aligned with and spaced apart from the susceptor for electromagneticallyinducing electric currents to flow within the flow section which providefor a substantially uniform thermal transfer across the flow section ofsusceptor to the material flowing through the flow ports; and whereinthe apparatus further comprises a thermal transfer member formed from anon-ferrous material and extending within the flow passage, downstreamof the susceptor, for transferring heat from the susceptor to a portionof the material after is passed through the susceptor.
 10. An apparatusfor heating a solid material to convert it to a liquefied material andfor dispensing the liquefied material, the apparatus comprising incombination:a central housing having an inlet, a dispensing orifice, anda flow passage extending through the central housing for passing theliquefied material from the inlet to the dispensing orifice; a susceptorhaving a conical flow section which extends across the flow passage andconverges toward the dispensing orifice, the flow section having aplurality of flow ports for passing the liquefied material therethrough;an induction coil disposed within the flow passage for immersion in theliquefied material, and being conically shaped to converge toward thedispensing orifice and partially surround the susceptor; and wherein theinduction coil electromagnetically induces electric currents to flowwithin conical flow section of the susceptor to heat and liquefy thesolid material.
 11. The apparatus according to claim 10, wherein theflow passage through the central housing defines an annular flow passagehaving a conical shape which extends between the susceptor and theinduction coil, and radial distances across the annular flow passageincrease as the annular flow passage converges toward the dispensingorifice.
 12. The apparatus according to claim 10, wherein the flowpassage through the central housing defines an annular flow passagehaving a conical shape which extends between the susceptor and theinduction coil, and the annular flow passage has a substantiallyconstant cross-sectional flow area as the annular flow passage convergestoward the dispensing orifice.
 13. The apparatus according to claim 10,wherein the flow ports are defined by substantially constant diameterholes which are spaced apart to provide a substantially constantcross-sectional flow area through the susceptor.
 14. The apparatusaccording to claim 10, further comprising:a thermal transfer memberformed from a non-ferrous material and extending within the flowpassage, downstream of the susceptor, for transferring heat from thesusceptor to a portion of the material after is passes through thesusceptor.
 15. The apparatus according to claim 10, furthercomprising:means for pushing the material relative to the susceptor andthrough the flow passage.
 16. An apparatus for heating a stick of glueabove a transition temperature at which the glue melts to change from asolid phase to a liquid phase, and for dispensing the glue in the liquidphase, the apparatus comprising in combination:a central housing havingan inlet for receiving the glue in a solid phase, a dispensing orificefor dispensing the glue in a liquid phase, and a flow passage extendingthrough the central housing for passing the glue from the inlet to thedispensing orifice; a susceptor having a conical flow section whichextends across the flow passage and converges towards the dispensingorifice, the conical flow section having a plurality of flow ports forpassing the glue therethrough when the glue is in the liquid phase,wherein the flow ports define a substantially constant cross-sectionalflow area through the conical flow section; wherein the susceptor andthe central housing together define an annular flow passage having aconical shape which extends therebetween, and the annular flow passagehas a substantially constant cross-sectional flow area as the annularflow passage converges toward the dispensing orifice; an induction coildisposed within the annular flow passage for immersion within the glue,and being conically shaped to converge toward the dispensing orifice andextend at least partially around the conical flow section of thesusceptor; and wherein the induction coil electromagnetically inducessubstantially uniform electric currents to flow within the conical flowsection of the susceptor to provide a substantially uniform thermaltransfer from the susceptor to the glue flowing within the flow ports.17. A method for heating, liquefying and dispensing a material, themethod comprising the steps of:providing a housing having a centralcavity, and a susceptor and an induction coil disposed within a centralcavity; placing the material within the central cavity on one side ofthe susceptor; passing an electric current within the induction coil tocause the induction coil to emit a electromagnetic field to thesusceptor, causing the susceptor to emit heat to the material; passingthe material through the susceptor to liquefy the material; and passingthe liquefied material through the induction coil, immersing theinduction coil within the material.
 18. The method according to claim17, wherein the coil is disposed downstream of the susceptor.
 19. Themethod according to claim 17, wherein the coil is disposed downstream ofthe susceptor and partially surrounds the susceptor.
 20. The methodaccording to claim 17, wherein the electric current is a high frequencyelectric current.